Improvement in the manufacture of carbonate of lead



NITED- STATES PATENT OFFICE.-

l IMPROVEMENT IN TH MANUFACTURE OF CARBONATE 0F LEAD, ac.

, Specifiiaatitinforming part of Letters Patent No. 1 12,608, dated March 14, 1871.

Be. it knowngthatglI, GEORGE T.LEWIS, of

the cityandlcounty of Philadelphia, in the ,Sta'teo'f Pennsylvania, have invented a new 1 and useful processof treating sulphate of lead with alkalinewcarbonates for the purpose of obtainingcarbonate of lead; and I do hereby declare the: following to be a full, clear, and

exact description thereof.

a My invention consists in the conversion of sulphate of lead intowearbonate through the intervention of carbonate of soda (whether in the form of soda-ash or carbonate of soda or sal-soda, or anyother of its commercial I forms) or the other alkaline soluble carbonates. chemically equivalent to carbonate of soda. :Toeifectthis change, I treat in the following mannerthe sulphateof lead, which is :now a refuseproductin certain technical op" erationsfor; whicnmay be readily or easily produced directly from the native sulphuret l of lead, also from the ores of lead and zinc *combined,-through aproper process of oxidiz-- ing, roasting; and burning 'A strong solution of carbonate 'of soda, with, say, at about 16;Baumsj Ihydrometer, which will be equivalent to ten per cent. of anhydrous or dry carbonatefls addedto the sulphate of lead .insuch amounts that for each atomof the sul- A. phate of lead there shall be represented in the solntionan atomof the soluble carbonate of e soda. This mixture is placed inaclosed iron vessel capable of'resisting the necessarypressnre, and suppliedlwithapressure-gage. Heat {I is then applied until apressure of, say, twenty- 1 five pounds to the square inch is attained with in the boiler. An interchange of acids and bases is effected withithe production of carbonateof lead and sulphate of soda.

The increased pressure has the double effect of increasing the activity of the chemical change A while at the same'timethe resulting carbonetc of lead is rendered more dense, and will betherefore: better adapted for employment as a pigment, since it has better covering prop erties; The product, which is a mixture of sulphate of soda with the carbonate of lead, is shown in a filter of suitable material, and

is well washed. The sulphate of lead is drawn ofi", leaving the carbonate of lead, which, after drying, is adapted for grinding in oil. If the sulphate of lead contains oxide of the same metal mixed With it, which is not uncommon when the sulphate resulting from the oxidizing roastings of galena or native sulphuret of lead is employed, the resulting carbonate also contains oxide and approaches very closely in composition to the white lead produced by the ordinary or Dutch method, the oxide-becoming hydrated under the increased pressure.

Instead of carbonate of soda, bicarbonate of soda orthe carbonates of pot-ash or ammonia or other soluble carbonate might be used,

although their cost would renderthem inferior to the carbonates of soda.

I do not limit myself to any special degree of pressure, but have expressed one which I find in practice gives a good result.

What I claim as my invention, and desire to secure by Letters Patent of the United States,

1. The manufacture of carbonate of lead or white lead directly from the sulphate of lead through the agency of the soluble carbonates heated under pressure.

2. As a new article of manufacture, car.-

bonate of lead produced by treating sulphate of lead wlth soluble carbonates. heated under pressure as the basis of a pigment or as amaterial to be used in the manufacture of acetates and other commercial. salts of lead or orange mineral or other commercial oxides of lead. 1

GEORGE T. LEWIS.

Witnesses:

WM. R. WRIGHT, THos. A.-BURTT. 

